feat: add message bus (.msg/) to codex team-lifecycle skill

Align codex version with Claude version's team_msg message bus for
frontend pipeline UI integration:

- Phase 2: create .msg/ dir, write meta.json with pipeline_stages/roles,
  init messages.jsonl with session event
- Phase 4: log task completion events, update role_state in meta.json
- Phase 5: update meta.json status to completed, log shutdown event
- SKILL.md: document .msg/ in session directory and add schema reference

.codex/skills/team-lifecycle/phases/05-completion-report.md

@@ -138,6 +138,27 @@ state.completed_at = new Date().toISOString()
 
 Write("<session-dir>/team-session.json",
   JSON.stringify(state, null, 2))
+
+// Update message bus meta.json status
+const meta = JSON.parse(Read("<session-dir>/.msg/meta.json"))
+meta.status = "completed"
+meta.updated_at = new Date().toISOString()
+Write("<session-dir>/.msg/meta.json", JSON.stringify(meta, null, 2))
+
+// Log completion event to message bus
+const msgCounter = getLastMsgCounter("<session-dir>/.msg/messages.jsonl") + 1
+logToMessageBus("<session-dir>", msgCounter, {
+  from: "coordinator",
+  type: "shutdown",
+  summary: `Pipeline completed: ${completedTasks}/${totalTasks} tasks (${successRate}%)`,
+  data: {
+    tasks_completed: completedTasks,
+    tasks_total: totalTasks,
+    success_rate: successRate,
+    duration_min: durationMin,
+    failed_tasks: failedTasks
+  }
+})
 ```
 
 ### Step 5.8: Output Completion Report